Display device containing minute droplets of cholesteric liquid crystals in a substantially continuous polymeric matrix

ABSTRACT

This disclosure is directed to articles of manufacture, chiefly display devices, containing minute &#39;&#39;&#39;&#39;naked&#39;&#39;&#39;&#39; droplets or inclusions of cholesteric liquid crystal material in a substantially continuous polymeric matrix, said liquid crystal material changing color or shade of color not only upon application of an electric potential but also upon removal of the field. The image produced has a comparable outline to that of the path of the electric field. Three chromatic states are evident, the normal color (before the electric potential is applied), the color given off when the electric field is applied, and the color observed when the electric field is removed. All three chromatic states are readily discernible from one another. The polymer matrix protects the cholesteric liquid crystal droplets from aging and enhances electric field behavior because the third chromatic state (electric potential removed) has a greater longevity with the matrix-bound material versus unprotected material of identical composition but no polymeric matrix. Other advantages are also discussed.

United States Patent Inventors Donald Churchill FOREIGN PATENTS f tDayton both of Ohio 1,484,584 5/1967 France 350/160 anes ar me 211 App].No. 707,706 OTHER REFERENCES I [22] Filed Feb. 23, 1968 J. H. Mu11erArticle on Effects of Electric FIelds on [45] Patented Aug. 17, 1971Cholesterol Nonanoate Liquid Crystals" In Vol. 2, of [73] Assignee TheNationalcash Register Company Molecular Crystals 1966 by Gordon &Breach. ScIence Daytomohio Publishers In Great BrItaIn, pages 167 188(pages 167 to 169 are sufficient for this case) 541 DISPLAY DEVICECONTAINING MINUTE 353 ;221:313; chi

' DROPLETS 0F CHOLESTERK: LIQUID CRYSTALS A!t0rney.r-E. Frank McKinneyand Joseph P. Burke IN A SUBSTANTIALLY CONTINUOUS POLYMERIC MATRIX 17Claims, 7 Drawing Figs. U-sn s t t n i t i t v s t s q I I s q i s I 1 st .I 250/435, 250/83, 252/316, 313/89 acture, chiefly display devices,containing minute naked [51] Illt. Cl 1/28, droplets or inclusions fcholesteric liquid crystal material i a H011 29/10 substantiallycontinuous polymeric matrix, said liquid crystal [50] Field Of Search313/108; material g g Color o Shade of color not ly p pp i 315/246;350/160; 23/230 LC; 252/3011; 250/71 cation of an electric potential butalso upon removal of the 1 field. The image produced has a comparableoutline to that of the path of the electric field. Three chromaticstates are [56] References Clted evident, the normal color (before theelectric potential is ap- UNITED STATES PATENTS plied), the color givenoff when the electric field is applied, ,2 1 1 /1 ner t l- 350/166 X andthe color observed when the electric field is removed. All 14,83612/1963 F gHS H 6i im-- 25 /8 three chromatic states are readilydiscernible from one 3,379,915 4/1968 Sentementes et al 313/108 another.The polymer matrix protects the cholesteric liquid 3,415,991 12/1968Asars 250/83 crystal droplets from aging and enhances electric field3,430,088 2/1969 Beswick 313/108 behavior because the third chromaticstate (electric potential 3,440,471 4/1969 Baczewski et al. 313/108removed) has a greater longevity with the matrix-bound 3,441,513 4/1969Woodmansee 252/408 material versus unprotected material of identicalcomposition 3,322,485 5/1967 Williams 350/160 but no polymeric matrix.Other advantages are also discussed.

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INVENTORS DONALD CHURCHILL 8 JAMES V. CARTMELL BY i W THEIR ATTORNEYSDISPLAY DEVICE CONTAINING MINUTE DROPLETS OF CI-IOLESTERIC LIQUIDCRYSTALS IN A SUBSTANTIALLY CONTINUOUS POLYMERIC MATRIX The presentinvention is directed to an article of manufacture for utilizing anelectric field to obtain an easily discemible, stable, and optionallyeither comparatively permanent or readily heat-erasable chromatic (colorand/or reflectance, viz, reflective intensity) representation ofcomparable outline to said electric field. Since the chromaticrepresentation is stable, it can serve a storage (memory) function. Oneof the particularly advantageous features of the present invention isthat the chromatic representation can be generated by a one-shot signaloutput, viz, an electronic computer output signal, a single sweep signalsuch as a radar scan, a display panel where information may be enteredonce for an extended period storage such as an air terminal scheduledisplay. Furthermore, the chromatic representation in the color stable(storage) state is capable of representing a fixed body or state ofinformation which can be retrieved and examined readily withoutrequiring continuous electric field potential, e.g., continuouspotential such as that obtained from an electron gun, e.g., cathode raytube, using conventional electronic computer equipment.

The article of this invention comprises, in its essential components, apair of spaced electrodes with a matrix-bound, droplet-containingcholesteric liquid crystalline member located in such a position thatthe electrodes impose an electric potential on said liquid crystalmember. Usually the electrodes are positioned such that the firstelectrode (the electrode closer to the viewing agency, e.g., eyes of theviewer) and second electrode (the electrode more remote from the viewingagency, e.g., viewer's eyes) are in electric fieldgenerating proximityto one another and the intermediate cholesteric liquid crystallinemember can, but need not, be in contact with the first and/or secondelectrode. Both direct current and alternating current can be employedto produce the electric field. The cholesteric liquid crystalline membercan be composed of a single substantially continuous polymermatrix-bound, naked droplet or inclusion of cholesteric liquidcrystalline material, but usually said member is composed of a plurality(and preferably a profusion) of individual, minute, naked droplets orinclusions of cholesteric liquid crystalline material. The term liquidcrystal," as used herein, is employed in the generic, art-recognizedsense to mean the state of matter often referred to as a mesophase,wherein the material exhibits flow properties associated with a liquidstate but demonstrates long range ordering characteristics of a crystal.The cholesteric liquid crystal refers to a particular type of mesophasemost often demonstrated by esters of cholesterol. Many of thecholesteric liquid crystals exhibit a reflective scattering of lightgiving them an iridescent appearance. The polymer matrix-boundcholesteric liquid crystalline droplet-containing member can be, andusually is, composed of droplets of a mixture of materials which form acholesteric liquid crystal. The term naked" as used herein refers to thefact that the droplets of liquid crystal material have no coveringexcept for the polymeric matrix in which they are located. Insofar asthe large majority of droplets are concerned, the polymer matrix iscontinuous, that is to say that the internally located droplets aretotally enveloped by a given portion of the matrix. Many of the dropletslocated close to the outer surface(s) of the matrix are likewise in acontinuous matrix of polymer material. Some of the droplets are on thesurface or a portion thereof has direct access to the open air throughan opening(s) in the polymer matrix. The term substantially continuous"accurately describes the polymer matrix which contains the vast majorityof liquid crystal droplets. At least one of the materials in thecholesteric liquid crystalline phase must be chromatically responsive toan electric field of the requisite intensity. Moreover, so long as thecholesteric liquid crystalline member is located intermediate (between)the electric field-imposing electrodes, the direction at which the fieldis applied to said member, viz, perpendicular or essentially parallel tothe direction of viewing is immaterial.

While the first and second electrodes need not be (and usually are not)coextensive throughout their entire extent and the cholesteric liquidcrystalline member need not be in direct contact with either or bothelectrodes; it is necessary for both the first and second electrodes tobe close enough to one another and to the intermediate cholestericliquid crystalline member to enable the formation of an electric fieldbetween the first and second electrodes. For most purposes, thecholesteric liquid crystalline member contains a cholesteric liquidcrystalline material which is chromatically responsive to an electricfield of from about 10,000 to about 1,000,000 volts per centimeter ofthickness of the cholesteric liquid crystalline droplet-containingmember. By chromatically responsive is meant that the cholesteric liquidcrystalline material (present in droplet form in the substantiallycontinuous polymer matrix defining the cholesteric liquid crystallinemember) must exhibit either an apparent change in color and/orreflective intensity (as viewed from incident white light) uponapplication of an electrical field of the above specified requisiteintensity thereto. Hence the term chromatic response is intended toinclude both changes (shift of wave length) in color and changes inintensity of reflectance of the same color so that it appears differentin color or shade of color from the previous color slate(s). Thus, asused herein, a change in color is synonymous with a change in reflectiveintensity and vice versa. The term apparent" is employed to denote thatthe color effect induced or brought about by the electric field, orsubsequent to its application, is different from the preexisting(natural) color or absence thereof present in the liquid crystals, perse. Usually the electric field employed will have an intensity rangingfrom about 20,000 to 200,000 volts per centimeter of thickness of theencapsulated cholesteric liquid crystalline member.

In addition to protecting the droplets of cholesteric liquid crystalmaterial, the substantially continuous polymeric matrix enables betteradhesion between the cholesteric liquid crystal member and the first andsecond electrodes or comparable contiguous surfaces. Also, the presenceof the polymeric matrix (which can be controlled to be of uniform andaccurate thickness) serves to enhance the optical homogeneity of thechromatic representation (image) observed in the display device.

CI-IOLESTERIC LIQUID CRYSTAL MEMBER While most, if not all, cholestericliquid crystal materials exhibit chromatic response to electricpotential; different cholesteric liquid crystals, and mixtures thereof,respond in varying chromatic contrasts at different electric potentialintensity levels. Of course, all changes in shades of color are notequally discernible to the naked eye. For this reason and others, e.g.,blindness" to certain colors and shades of colors; it is within thepurview of this invention to use specific color filters and opticalsensors to aid in detection of subtle changes in shades of color andconvert these subtle changes to more clearly recognizable ones. Hence,while all cholesteric liquid crystals are not equal in chromaticresponse to electric potential for display purposes when the display isviewed by the naked eye; deficiencies in clearly observable contrast canbe compensated for. Nevertheless, for most visual display devices it ispreferable to employ cholesteric liquid crystals whose chromaticresponse is both clearly discernible to the naked eye and in sharpchromatic contrast to its preceding color state.

When an electric field is imposed on the matrix entrapped droplets ofcholesteric liquid crystal material, the liquid crystals change color(or reflective intensity) substantially instantaneously (2010milliseconds) to shift from a first chromatic state (that normal colorstate existing prior to the application of an electric field thereto) toa second chromatic state, viz, the chromatic state existing due to thepresence of the electric potential. The second chromatic statedemonstrates a color (or reflective intensity) different from that ofthe first chromatic state, and this difference is preferably readilyrecognizable to the naked eye. Upon removal of the electric field, thecolor changes from the second chromatic state to a third chromatic stateand the color (or reflective intensity) exhibited by the liquid crystalmaterial in the third chromatic state is different from that of thecolor given off in the second chromatic state and first chromatic state,respectively.

A very unusual and advantageous feature of a preferred embodiment of thepresent invention resides in the fact that the third chromatic statedisplays a stability and permanence colorwise, viz, it does not readilyfade" back to the first chromatic state. Compared with unprotectedcholesteric liquid crystals, the matrix entrapped cholesteric liquidcrystal droplets have the ability to retain the third chromatic state inmost cases for at least several orders of magnitude of time longer thanthe unprotected material. This retention ability can be employed instoring information for future use.

An example of the difference between the color or reflective intensitybetween the three chromatic states spoken of hereinabove can be gleanedfrom the following illustrative example. Using the mixture ofcholesteric liquid crystalline materials noted below in Example 1, anoriginal or first chromatic state which is a green color is observed tothe naked eye. Then, when the electric potential is applied so as tocreate an electric field between the first and second electrodes, thesecond chromatic state produced is a blue-green color quite distinct inappearance to the naked eye from the first chromatic state. Then, whenthe electric field potential is removed, a third chromatic state isproduced which is, to the naked eye, a grey color, which is quitedistinct in appearance from both the green of the first chromatic stateand the blue-green of the second chromatic state.

Suitable chromatically responsive cholesteric liquid crystal materialsinclude, but are not limited to, the following: cholesteryl halides,e.g., cholesteryl chloride, cholesteryl bromide and cholesteryl iodide;cholesteryl nitrate and other mixed esters of cholesterol and inorganicacids; cholesteryl esters of saturated and unsaturated, substituted andunsubstituted organic acids, esp, cholesteryl esters of C to Caliphatic, monocarboxylic acids, e.g., cholesteryl nonanoate,cholesteryl crotonate, cholesteryl chloroformate, cholesterylchlorodecanoate, cholesteryl chloroeicosanoate, cholesteryl butyrate,cholesteryl caprate, cholesteryl oleate, cholesteryl linolate,cholesteryl linolenate, cholesteryl laurate, cholesteryl erucate,cholesteryl myristate, cholesteryl clupanodonate, oleyl cholesterylcarbonate, cholesteryl heptyl carbamate, decyl cholesteryl carbonate;cholesteryl esters of unsubstituted or halogenated aryl, -alkenaryl,-aralkenyl, -alkaryl and -aralkyl organic acids, especially cholesterylesters of those organic acids containing an aromatic moiety and from 7to 19 carbon atoms, such as, cholesteryl p-chlorobenzoate, cholesterylcinnamate; cholesteryl ethers, e.g., cholesteryl decyl ether,cholesteryl lauryl ether, cholesteryl oleyl ether, etc.

As mentioned above comparatively pure, chromatically electric potentialresponsive cholesteric liquid crystalline materials, viz, individualchromatically responsive compounds, can be used; or the chromaticallyelectric potential responsive materials can be used in admixture. Theuse of such mixtures is actually preferable in many cases because withmixtures the liquid crystalline state can be maintained more readily atambient room temperatures without requiring extraneous heating. On theother hand when an individual chromatically responsive compound isemployed, it i frequently necessary to heat the immediate environment(where the device is to be employed) in order to maintain the materialin the liquid crystal state because many such materials are solids atambient room temperatures. For most applications the chloro derivativesare preferred due to their ability to produce color changes (or shiftsin reflective intensity) readily recognizable to the naked eyeespecially in the second and third chromatic states mentionedhereinabove. Some exemplary mixtures of cholesteric liquid crystalmaterials which can be employed in accordance with this inventioninclude, but are not limited to, the following: cholesteryl nonanoate,cholesteryl chloride and cholesteryl cinnamate; cholesteryl nonanoateand cholesteryl chloride; cholesteryl nonanoate and cholesteryl bromide;cholesteryl nonanoate, cholesteryl bromide and cholesteryl cinnamate;cholesteryl nonanoate, cholesteryl iodide and cholesteryl cinnamate;cholesteryl nonanoate, cholesteryl iodide and cholesteryl benzoate;cholesteryl nonanoate, cholesteryl chloride and oleyl cholesterylcarbonate; cholesteryl nonanoate, cholesteryl chloride, oleylcholesteryl carbonate and cholesteryl bromide; oleyl cholesterylcarbonate and cholesteryl iodide, oleyl cholesteryl carbonate andcholesteryl p-chloro benzoate; etc.

Also, it should be understood that included within the term cholestericliquid crystalline mixtures are mixtures of two or more individualmaterials, one or more of which individually does not form a cholestericliquid crystal phase but which in admixture exhibit a cholesteric liquidcrystal phase. Hence, two or three materials which individually are notcholesteric liquid crystals can be employed in accordance with thisinvention if, when in admixture, they do exhibit cholesteric liquidcrystal behavior, viz, they form a mesophase which demonstrates theproperty of reflection light scattering. One such mixture is cholesterylnonanoate, oleyl cholesteryl carbonate and cholesterol. The lattermaterial, by itself, does not form a cholesteric liquid crystallinephase; but does so in combination with the other cholesteric materials.

Various natural and synthetic film-forming polymeric materials can beemployed to constitute the polymeric matrix, film or coating in whichthe individual droplets or inclusions of cholesteric liquid crystalmaterial are located. Any transparent or substantially transparentfilm-forming polymeric material with adequate electrical insulationproperties and which is soluble in a liquid which does not dissolve orsubstantially chemically affect the liquid crystal material adverselycan be used. Suitable representative film-forming polymeric materialsfor this purpose include, but are not limited to, the following:polyvinyl alcohol; gelatin, gum arabic, zein, a prolamine film formerderived from the alcohol extraction of zea mays, a grain commonly calledIndian corn; hydroxy ethyl cellulose; polyvinyl pyrrolidone;polyethylene oxide; copolymers of ethylene and maleic anhydride;copolymers of vinyl methyl ether and maleic anhydride; etc. Thecholesteric liquid crystals can be dispersed or positioned within thepolymer matrix conveniently by emulsifying minute droplets of liquidcrystal material in a dryable liquid solution of the film-formingpolymeric material which is to constitute the polymer matrix. Accordingto a preferred embodiment of this invention, the droplets of liquidcrystal material are emulsified in an aqueous solution of film-formingpolymer. Since an extremely small droplet size of cholesteric liquidcrystal material can be maintained in an emulsion, coatings or filmsprepared therefrom allow a good optical resolution and have a smoothsurface(s). These characteristics enhance the optical or visual readoutof display devices containing the droplets in the matrix. In general,individual droplet size can range from about 0.5 to about 50 microns,but usually the individual droplet size ranges from about 1 to about 30microns. Average droplet size can range from about 1 to 30 microns butusually ranges from about 5 to about 20 microns. Films prepared bydrying these emulsions, containing the minute individual liquid crystaldroplets or inclusions, can be stained or tinted as desired to enablethe polymer matrix to serve as a color filter for light traveling to andfrom the liquid crystal material. Such a system can be used where anarrowing of the broad iridescent effect present in some liquid crystalmaterials in the second and third chromatic states is desired. Moreover,such films can also be pigmented slightly, but care should be .exercisedto avoid use of an excessive amount of pigment or other nonlightreflecting material as it can diminish the color response and brilliancedue to interference with incident and reflected light.

Comparative tests between polymer matrix-protected cholesteric liquidcrystal materials versus films of unprotected liquid crystal materialsof identical composition reveal several important advantages for thefilms comprised of droplets of cholesteric liquid crystal material in asubstantially continuous polymer matrix when employed in the articles ofthis invention. One of the major advantages resides in the apparentprevention of crystallization of the liquid crystals and mixturesthereof, or at least a diminution in the tendency towardscrystallization. Hence, many cholesteric liquid crystal materials andmixtures are normally solid at room temperature. These mixtures oftensupercool considerably so that crystallization is not immediate atambient room temperatures. However, they do crystallize within a day ora longer time period and must be reheated to the liquid crystaltransition temperature range in order to be suitable for display, forexample in chromatic image recognition use. The dispersion of thesemixtures in the polymer matrix seems to inhibit crystallization, and thecholesteric liquid crystal materials when dispersed within said polymermatrix are observed to remain in the liquid crystal state for a longerperiod of time than pure film of the same materials (no polymer matrix).

Another advantage attainable in the articles of the present invention isthe ability of the matrix-entrapped material to retain the thirdchromatic state for comparatively permanent periods of time versus thecomparatively transitory retention of the third chromatic state in thecase of unrestrained cholesteric liquid crystals.

A further and equally important practical advantage of use of thematrix-retained droplets of cholesteric liquid crystals is their abilityto be used in multicomponent (multicolor) systems, viz, as coatings orincorporated in a matrix containing a plurality of different cholestericliquid crystalline mixtures, each mixture giving a characteristic colorthroughout the three chromatic stages referred to hereinabove with thedifferent mixtures being employed in close proximity so that amulticolored display is achieved in one, two or all three chromaticstates. Moreover, polychromatic displays can be achieved by using aplurality of switched leads or contacts. In one case, some switches canbe turned on and the others left off which creates a polycolored effectusing differently colored mixtures or one mixture. Another way toachieve such an effect is to use a plurality of mixtures each of whichis responsive at a different level of intensity of field potential toexhibit a different apparent color or shade of color. Yet another way ofachieving the polychromatic displays is tohave some switches turned onand then turn a portion of them off so that some switches are on, andsome switches are off (never having been turned on) some of which werepreviously on. This works well with a single cholesteric liquid crystalmaterial, one mixture or a plurality of differently colored mixtures.

A still further advantage of the articles of the present inventioninclude their processing flexibility in that a wider range of devicescan be prepared to meet a wider range of specifications. For example,electric field sensitive display devices utilizing polymermatrix-retained cholesteric liquid crystal droplets can be prepared tobe either flat or curved, and either rigid or flexible. In the case ofpure" cholesteric liquid crystal films, for all practical purposes theyrequire two flat, rigid, evenly spaced electrodes. Of course, theseuse-limiting requirements are not applicable to the matrix-retainedproducts because the substantially continuous polymer matrix furnishesthe uniform support to the extent required, yet can be flexible enoughto accommodate complex shapes. Yet

.another advantage attendant to the articles of this invention is thatthe polymer matrix not only protects the cholesteric liquid crystallinematerial, e.g., from deleterious orientation and other adverse surfaceeffects, but due to the extremely small droplet size which can bemaintained in an emulsion also substantially supplies a uniformthickness to the film thereof since the coating provides the droplets ina condition of roughly uniform diameter. This results in smooth coatingsof good optical resolution.

Until recently the utility of cholesteric liquid crystals was limiteddue to disadvantages, including the following ones:

1. Some systems containing a mixture of one or more intermingledcholesteric liquid crystal compounds, as a film, are subject tocrystallization of large areas at the desired working temperatures. Thisundesirable crystallization tends to concentrate one of the activematerials at each crystallization site to thereby separate it from theother components of such a mixture. In turn, component separationresults in loss of precision and efficiency of color change;

2. Most cholesteric liquid crystal materials which are chromaticallyresponsive to an electric field are cholesterol derivatives which areoily liquids at and above their melting temperatures. When they exist asa film on any surface, the film (being wet) is subject to injury andcontamination, e.g., form aging and contact with the environment. Thus,dust particles are easily entrapped by the liquid surface and can serveas undesirable nucleation sites for crystallization. Also such films areexposed to contact with any material in the vicinity with resultantdisorganization and possible change of thickness in localized areasthereby altering chromatic response;

3. The flow of such liquid crystal films between electrodes;

4. The formation of bubbles due to electrical breakdown of thecholesteric liquid crystal material;

5. Nonuniform optical and electrical surface effects exhibited at theelectrodes, e.g., orientation at the surface of the cholesteric liquidcrystal film. The present invention overcomes or alleviates most, if notall, of these problems.

The total (overall) thickness of the cholesteric liquid crystallinemember can range from about 0.001 to about 0.05 centimeters (notcounting the thickness of any optional protective film applied thereto).Usually the film thickness of the cholesteric liquid crystalline memberranges from about 0.003 to about 0.01 centimeters and preferably fromabout 0.005 to about 0.01 centimeters. The film can be of a thickness toinclude only a single layer or a few layers of liquid crystal droplets;or the film can include a larger number of layers thereof, within itsthickness.

FIRST ELECTRODE While both electrodes can be composed of nontransparentmaterial or presented in nontransparent form (not FIG. 4); it is usuallypreferable that the first electrode be transparent.- In such cases thefirst electrode can be formed of any transparent electroconductivematerial. For practical considerations, it is usually desirable to formthe transparent first electrode as thin as possible, in order to obtaina combination of maximum transparency and yet retain electricalcontinuity of the electrode. According to a preferred embodiment of thisinvention, the transparent first electrode can be composed oftransparent metal or metal oxide films, coatings or otherelectroconductive layers. Suitable metal and metal oxide materials whichcan be employed for this purpose include, but are not limited to, thefollowing: tin oxide, gold, platinum, chromium, nickel. In the case ofmetallic materials, transparent film can be made by using very thinhomogeneous coatings or preparing a series of very thin, closely spacedribbons of the metal by photoetching away -90 percent or more of thematerial. A more comprehensive listing of suitable transparent metal andmetal oxide electric conductive films can be found in US. Pat. No.2,628,027 to Colbert et al., the disclosure of which is incorporatedherein by reference. The deposition of the transparent electrode can beupon a protective inorganic, e.g., glass, or organic, e.g., acrylate oralkyl acrylate polymer plastic or other polymeric protective basematerial, which then constitutes the upper or viewing surface throughwhich the cholesteric liquid crystalline member's chromatic response tothe electric potential is viewed. Various transparent plastic andresinous protective layers can be first pr0- vided with a transparentelectroconductive layer by known coating or deposition techniques, suchas, e.g., those indicated in any one of the following US. Pat. Nos.:2,704,265; 2,739,083; 2,740,732; 2,750,832; 2,758,948; 2,904,450;2,907,672; 3,001,901 and 3,020,376. During assembly the transparentfirst electrode is placed in direct contact with the cholesteric liquidcrystalline member. Other suitable exemplary procedures for depositingelectroconductive coatings upon the glass or plastic base includethermal sputtering or evaporative coating using metal halide solutionsfrom a vacuum to which oxygen is then supplied in order to oxide themetal halide salt and form the metal oxide film in situ upon the desiredbase material. Other satisfactory conventional techniques are used whenforming metal coatings, e.g., by chemical reduction, viz, coating metalsalt solution containing a reducing agent to reduce the metal salt toyield the metal film (one step procedure) or coating a metal salt ontothe base, followed by a second coating using a solution containing areducing agent (two step procedure), the latter procedure being similarto that used to form silver mirror films. Other satisfactory coatingprocedures will be apparent to those skilled in the art. When the firstelectrode is nontransparent, e. g., in the form of a thin,electron-emitting, resistive wire(s) as in FIG. 4; the wire(s) can bepositioned so as not to obstruct or interfere substantially with theobserved image.

SECOND ELECTRODE The second electrode can be composed of anyelectroconductive material and need not be transparent; nor need it becoextensive with the first electrode throughout its entire extent. Infact, usually the second electrode is neither transparent norcoextensive with the first electrode. For example, the second electrodecan be imposed in the pattern of a printed circuit or it can have anydesired configuration. Hence, the second electrode can be deposited intransparent, nontransparent or partially transparent form, using suchmaterials as copper, silver, gold, iron-containing metal alloys, carbonblack, graphite, lead sulfide, etc.

In order to aid in viewing the chromatic representation produced uponthe cholesteric liquid crystalline member through the imposition of theelectric potential thereto, it has been found desirable to provide anopaque, e.g., black contrasting background behind the cholesteric liquidcrystalline member, e.g., either in front of or behind the secondelectrode. The reason for this is that the chromatic change which theliquid crystals undergo is observable through light scattering, viz, thescattering of light through the strata of the liquid crystallinematerial. Hence, in order to observe the chromatic changes properly, itis most advisable to provide a black, lightabsorbing background. Thatbackground can, itself, be an electrode, e.g., be prepared from blackpaints, black dye, etc., containing an electroconductive component suchas carbon black or black anodized metal. The black background is notalways necessary however. Note the description in conjunction with FIG.6 in this respect.

In many cases (e.g., FIGS. 2, 3, 5 and 6), it is preferable to employ aninsulating glass, plastic or other transparent or substantiallytransparent material as a protective layer on top of the transparentfirst electrode. Suitable materials from which this protective layer canbe made include, but are not limited to, the following: Various types ofglass and inorganic ceramics, such as conventional soda-lime-silicaglass; lithia-sodalime-silica glass; potassia-soda-lithia-alumina-silicaglass, various organic glass and other transparent organic polymericmaterials, such as the methacrylate and alkylmethacrylate andalkylacrylate plastics, e.g., polymethylmethacrylates,polyethylmethacrylates, polymethylacrylates, polyethyl acrylates, andother acrylic acid and methacrylic acid homo and copolymers. Othertransparent or substantially transparent insulating protective materialssuitable for use will be apparent to those skilled in the art.

In order to supply an electric potential to the first electrode andsecond electrode, it is practical and convenient to locate conductiveelements (leads) in electroconductive contact with both of saidelectrodes. Thus, one or more conductors will be located in directcontact with the first electrode and one or more other conductors willbe in contact with and preferably located behind the second electrode. Aprotective layer of glass, plastic, or other electrically insulatingmaterial (not necessarily transparent) can be employed as a surfacinglayer to protect that side of the article in close proximity to saidsecond electrode and the conductive element(s) or leads in contacttherewith.

ILLUSTRATIVE DEVICES The present invention will be understood in greaterdetail in conjunction with the attached drawings. FIG. I of the drawingsis a cross-sectional view through a liquid crystal member or component.FIG. 2 is a cross-sectional view through one embodiment of the presentinvention which illustrates a display device. FIG. 3 is likewise across-sectional view of an article of this invention illustrating analternative display device. FIG. 4 is a cross-sectional view of a vacuumtube display device wherein the field is supplied by electrons drawn tothe surface of the liquid crystalline member. FIG. 5 is a crosssectionalview through a cathode-ray tube containing the structure of the presentinvention and serving as a display device. FIG. 6 is a cross-sectionalview of an alternative form of cathode-ray tube utilizing the presentinvention. FIG. 7 is a cross-sectional view of yet another deviceillustrative of this invention wherein both an electric field andthermal energy can be utilized to impose transient and/or comparativelypermanent colored images on the same cholesteric liquid crystal member.Optionally selected images can be stored and others erased. Transientimages (imposed by heat) can be changed at will on a stored imagebackground of contrasting color.

FIG. 1 shows the presence of cholesteric liquid crystal member 3comprised of a plurality of minute, individual, naked" droplets orinclusions, a, of cholesteric liquid crystal material confined within asubstantially continuous matrix, b, of polymeric material. The dropletshave a random shape and are reasonably uniformly distributed (dispersed)within the polymer matrix. An optional thin, protective barrier film,e.g., polyethylene glycol terephthalate Mylar polyester can be depositedon one or both major surfaces of liquid crystal member 3 to preventdeleterious solvation of surface located liquid crystal material, e. g.,by a solvent component(s) such as may be contained in opaque lacquerfilm 4 of FIG. 2. As shown in FIG. 2, transparent (glass or plastic)insulating protective layer 1 is directly in contact with transparentfirst electrode 2 which in turn is in intimate contact with thecholesteric liquid crystalline member 3. The cholesteric liquidcrystalline member 3 is composed of an array or profusion of minutedroplets, a, of cholesteric liquid crystalline material retained withina substantially continuous polymeric matrix, b, with or without aprotective barrier film (not shown) on one or both sides thereof. Inaddition to enhancing the optical properties of the liquid crystallinemember and protecting the droplets from deleterious exposure, thepolymeric film, b, serves as an effective insulator between both of saidelectrodes. Next to the cholesteric liquid crystalline member 3 islocated a black lacquer insulating film 4 to enhance the observation ofthe chromatic changes in the liquid crystalline member. Conductiveelements 5 are located intermediate between lower protective layer 6(usually glass or plastic) and black insulating film 4. While FIG. 2shows three such elements, it should be clearly understood that anydesired number can be used and the configuration thereof can be arrangedin any desired display pattern, sequence or shape. Upper and lowerelectrodes (leads) 7 and 7', respectively allow the passage of anelectric current from a suitable-potential source (not shown) intoelectroconductive contact with both the first transparent electrode andthe conductive elements 5. Upon subjecting the liquid crystalline memberto the electric field by applying an electric potential across the leads7 and 7; the chromatic representation viewed through the transparentlayers of 1 and 2 will conform closely with the configuration defined bythe field established between conductive elements and the top electrode.That is to say that the configuration established by the elements 5 willbe reproduced, but in different color or intensity of reflectance fromthe surrounding film areas when looking down through the transparentprotective layer 1 and transparent first electrode 2. Upon opening thecircuit, a further chromatic change takes place in the configurationareas wherein the cholesteric liquid crystalline material rapidlychanges from the second chromatic state to the third chromatic statecharacterized by the ability of the cholesteric liquid crystallinemember to retain a substantially permanent and different chromatic statefor extended periods of time under normal atmospheric conditions oftemperature and humidity. If desired, a sealer tape or potting compound(not shown) can be applied to the outer peripheral edge(s) to aid insealing the various layers against lateral and interfacial exposure tothe atmosphere at the peripheral edge surfaces.

FIG. 3 illustrates an alternative display device and is comprised oftransparent glass plate 1 in contact with transparent electroconductivefilm 2 which in turn is in contact with liquid crystalline member 3,which is composed of a profusion of minute cholesteric liquid crystaldroplets or inclusions present in a retaining matrix of insulatingpolymeric film. Black insulating film 4 is deposited by coating on thecholesteric liquid crystalline member 3 throughout its entire extent.Electroconductive film 5' (as deposited in any desired configuration toconstitute for example a printed circuit or portion thereof) isdeposited in intimate contact with black insulating layer 4. A conductorlead wire 8 is attached to or made integral with conductor film 5.Leads, 7 and 7 are attached to bus bars in contact with the transparenttin oxide electroconductive film 2 at the leftand right-hand sides,respectively, thereof. Upon application of potential across the uppertransparent electrode 2 and the lower electroconductive film 5 throughthe intermediate cholesteric liquid crystalline member 3, the visualchromatic image corresponding to the configuration of printed circuitelectroconductivefilm 5 appears to the viewer through the protectivelayer 1 and transparent electroconductive film 2, thereby exhibiting acolored image, the first, second (potential on) and third (potentialoff) chromatic states of which will depend upon the composition of theselected cholesteric liquid crystal material or mixtures thereof. Onpassing a current through leads 7 and 7 through the upper tin oxideelectrode, the upper electrode can be heated to the isotropic transitiontemperature of the cholesteric liquid crystals thereby erasing the imageproduced during the third chromatic state. Upon cooling to ambient roomtemperatures, the liquid crystals then return to their original (first)chromatic state. Hence, it will be seen that this invention allowsstorage of information until desired followed erasure-followed-byimposition of new, e.g., updated information all accomplishedelectronically on a one-shot basis without the necessity for continuouselectronic output during either storage or erasure.

F IGv 4 illustrates an article of the present invention wherein thefield is established by electrons attracted to the surface of thecholesteric liquid crystal-containing film. A matrix of conductiveelements, 5, is supported on insulator, e.g., fiberglass substrate in avacuum tube 9 with a transparent viewing port or face plate 10. Theconductive elements are held at a positive potential by means ofconnecting the leads 13 to a potential source (not shown). A current ispassed through thin, nontransparent resistive wire 12, so that it isheated and emits electrons. The electrons are drawn to the surface ofthe liquid crystal film 3, directly over the positively chargedconductive elements. The field formed between the surface electrons andthe conductive elements causes the liquid crystal to change color. Asshown here, three lead elements are used but it is possible to use anydesired number and configuration of elements to describe the patterndesired. After the potential is removed from the elements, 5, thepattern will remain until erased by heating to the isotropic transitiontemperature. This can be accomplished by means of any suitable energysource, e.g., heat lamp, heat wires or passing a current through theconductive elements.

The device of FIG. 5 is a conventional cathode-ray tube envelope 9(C.R.T.) with a transparent conductor 2 coated on the inner surface ofthe transparent face plate 10. A film 3 of a profusion of minutedroplets of cholesteric liquid crystal confined in a polymeric matrix iscoated in direct contact with the transparent electrode 2 on the innersurface of the face plate, and a black insulator film 4 is coated on theliquid crystal film. The transparent electrode 2 is held at a positivepotential via lead 7, and electrons from the electron gun 14 are causedby suitable deflection techniques to impinge on the black insulator inthe desired pattern. The local fields set up between the electrons atthe insulator and the front electrode cause the liquid crystal to changecolor in those areas forming a visual pattern when viewed from the frontof the tube. The pattern is semipermanent and one sweep of the electronbeam will suffice to establish a permanent image. This image can beerased by heating the liquid crystal above its isotropic transitiontemperature. A suitable way to do this is to pass a current through thetransparent electrode as described in the previous illustration.

In the device of FIG. 6 a conventional C.R.T. is prepared with amultitude of conductive wires 15 extending through the face plate 10 andflush with the outer surface on the face plate, A black insulating film4 is formed on the face plate and the liquid crystal film member 3 iscoated on the insulator. A transparent protective outer plate 1 uponwhich a transparent conductive electrode 2 has been deposited is broughtin contact with a liquid crystal film with the conductive surface inclosest proximity to the liquid crystal member. The transparentelectrode 2 is held at a positive potential via lead 7. The electronsfrom the electron gun 14 are deflected by any suitable conventionaltechnique such that they describe a pattern on the inner surface of theC.R.T. face plate. The electrons striking the wires 15 are drawn to theinsulator film 4 and local fields are established across the liquidcrystal film 3 between the charged wires 15 and the outer transparentelectrode 2. The liquid crystal in these areas will demonstrate a colorchange visible to the viewing agency, A.

As previously stated, the black insulating layer is often used to absorblight transmitted through the liquid crystal film and thereby increasethe contrast of the liquid crystal colors. This light absorbing layer isnot always necessary for adequate contrast in this type of a C.R.T.display device however.

In the device of fig. 7, transparent electroconductive coating 2, e.g.,tin oxide, is deposited on transparent protective element 1, which alsoserves as a substrate or support for the coating. Bus bars 7, 7 areattached along the edges of coating 2 and have conductive leads L, L,respectively, attached thereto. Opaque, e.g., black, nonreflectiveinsulator film 4 has a layer or film 3 containing a profusion of minutedroplets of cholesteric liquid crystal material confined within apolymeric matrix deposited thereon. Resistive conductor elements 5 canbe deposited directly on insulator 4, or on a lower supportive andprotective layer (not shown), such as layer 6 of FIG. 1. The cholestericliquid crystal member 3 is positioned in contiguous or closely spacedrelationship to coating 2. Each resistive element 5 has a pair of leads8, 8' attached thereto, thus enabling each resistive element 5 to beoperable separately or in groups, e.g., by appropriate conventionalswitching. Resistive elements 5 can be formed, or deposited, in anydesired configuration or design. The device of FIG. 6 has two primarymodes of operation (A) and (B), as follows: (A) Field effect mode ofoperation with image storage and erasure;

An electric field is applied across the liquid crystal film by apotential applied to the top conductive coating 2 and any one or more ofthe resistive elements 5. The liquid crystal transforms to the secondchromatic state in the area of electric field imposition. After thefield is removed; it assumes the third chromatic state in the areas overthe resistive elements 5. These areas can be selectively erased bypassing a current through the rear resistive elements, thereby heatingthe liquid crystal to the isotropic melt temperature. On cooling, thoseareas which had been heated return to the first chromatic state and asemipermanent (stored) pattern is displayed from the areas over theelements which were not thermally erased.

When it is desired to change the stored image; the remaining resistiveelements can be heated or the entire display unit can be heated bypassing a current through the top conductive coating 2 to effecterasure. This mode of operation is more complex for dynamic display buthas the advantage that the field can be applied to all the resistiveelements at one time and individual switches to these elements are notrequired. (B) Thermal mode of operation with storage option;

The device is operated thermally in the following manner:

An electric current is passed through the resistive element by means ofseparate pairs of leads 8, 8' for each such restive element. The heatingof each element raises the temperature of the encapsulated liquidcrystal directly above the element to the isotropic melting point.The'heated portion becomes nonreflecting in contrast to the coloredappearance of the unheated areas. When the current is interrupted, theelement cools to ambient temperature and the liquid crystal returns toits initial colored (first chromatic) state. Thus different charactersand designs (corresponding in shape and size to that of resistiveelements 5) can be displayed in a transient manner.

When it is desired to store an image; one of the leads 8, 8 is connectedto a high voltage source (not shown), and the other side of this sourceis connected to the transparent top electrode 2, through either of leadsL, L and their associated bus bars 7, 7'. A field generated across theliquid crystal film will cause a color change over the chosen resistiveelement 5; and when the field is removed, the electric field inducedcolored image will remain in the third chromatic state.

Erasure of this image can be accomplished readily by heating the liquidcrystal member to the isotropic melting temperature either by heatingonly those elements 5, which were used to generate the field or bypassing a current through the top conductive coating 2, by applying apotential across leads L, L. On cooling, the liquid crystal film returnto its original (first) colored state. Other operational modes will beapparent to those skilled in the art.

Hence it will be apparent that the device of FIG. 7 is, in effect, adisplay device having polychromatic capability for chromaticallyrepresenting an optionally comparatively permanent (third chromaticstate) yet thermally erasable configuration established by an electricfield in optional conjunction with an independently operable yetthermally erasable transient, thermally operable, separate display meanswherein said device comprises a transparent support 1; a transparent,electroconductive coating 2 on said support; conductive electrodes 7, 7in contact with said coating and operatively connected by leads L, L toan electric field source; an insulator film 4 having a cholestericliquid crystal member 3 in intimate proximity to said film and saidcoating; at least one electrically conductive resistive element 5 inthermally responsive association with said member, each said resistiveelement having a separate pair 8, 8' of conductive leads connected to acurrent source operable independently from said electric field sourceand wherein said cholesteric liquid crystal member is chromaticallyresponsive to both an electric field and thermal energy applied thereto.

FORMATION OF CHOLESTERIC LIQUID CRYSTAL MEMBER crystal materialdispersed in a substantially continuous solid polymeric matrix. Thesemembers can be prepared readily by dispersing (emulsifying) minutedroplets of cholesteric liquid crystal material in a dryable liquidsolution of film-forming polymeric material and then coating, casting orotherwise depositing the solution upon the desired surface. Also films,sheets, layers, etc., can be preformed, e.g., by casting, and thenassembled into the composite structure at the desired time. Coating andcasting solutions can be prepared readily by adding the cholestericliquid crystal compound or mixture' to a solution, e.g., aqueoussolution of film-forming polymer matrix material, e.g., polyvinylalcohol, using a stirrer, mixer, blender or equivalent agitation deviceuntil a liquid crystal droplet size range of from about 5 to about 20microns is obtained. This emulsion can be coated on the substratedirectly, e.g., by means of a draw-down applicator, onto a blackenedsubstrate, e.g., of Mylar" (polyethylene glycol terephthalate) to a wetfilm thickness of about 10 mils (0.0254 cm.) and air dried, e.g., atabout 25 centigrade. Film thickness can be increased by repeatedsequences of coating and drying. The dried emulsion film can be strippedfrom its substrate and utilized as a preformed film which can beoptionally opacified or blackened for use in the articles of thisinvention. Various mixtures of cholesteric liquid crystals can be usedwith various polymeric film-forming matrix materials. In accordance withthis invention films can be formed which contain from about 30 to about95 weight percent of cholesteric liquid crystal material, in dropletform, with the remainder being polymer matrix material. Usually,however, the liquid crystal droplets represent from about 50 to aboutweight percent of the total film weight (droplets plus polymer matrix).

Layers cast from an emulsion of the liquid crystal material and thendried are dry to the touch (although containing liquid inclusions; arerelatively unaffected by brushing contact with foreign bodies; aresubstantially immune to solute contamination, e.g., absorption ofextraneous vapor; and are not subject to rapid deterioration byselective nucleation crystallization; and, in cases wherecrystallization does begin, it is stopped from further areawisedevelopment by a boundary of the polymer matrix.

'Additional information on preparation of cholesteric liquid crystalmembers can be found in US. Pat. application Ser. No. 861,197 filedSept. 25, 1969 which is a streamlined continuation of US. Pat.application Ser. No. 618,895, filed on Feb. 27, 1967 by Donald Churchillet al. now abandoned. The disclosure of this application is incorporatedherein by reference.

Another feature of the incorporation of polymer matrix bound droplets ofthe cholesteric liquid crystalline materials into a system to provide anelectric potential-activated sensing or display device is theutilization of various mixtures of liquid crystals as to droplet sizeand chromatic response for indicating and/or displaying a wide range ofspecific levels of electric potential. Such a system, in one case, cancomprise a plurality of layers, each layer comprising one, two or moretypes of droplets having different mixtures of chromatically responsivecholesteric liquid crystalline materials. These devices can be tailormade to accomplish the desired task by variation of characteristicsimparted thereto by any one of the following adjustments; (a) electricfield response range; (b) size of the liquid crystal droplets; (c) typeand thickness of the polymer matrix material; (d) specific compositionof the cholesteric liquid crystalline material(s), and the like, all tothe purpose of choosing a response suitable for a given proposed use.

The present invention will be illustrated in greater detail in thefollowing examples which are included herein for illustrative purposesand should not be interpreted as limiting the present invention.

All percents and parts are by weight unless noted otherwise.

EXAMPLES 1-4 Cholesteric members comprised of droplets of cholestericliquid crystal material confined in substantially continuous solidpolymer matrices are prepared using the below tabulated variety ofspecific matrix and liquid crystal materials. In each case 60 grams ofcholesteric liquid crystal material is disposed in 100 cubic centimetersof the aqueous polymer solution in a Waring blender heated to 70centigrade by a heating jacket. Upon dispersion and formation of thedesired emulsion droplet size (in the range of l to 50 microns), thevarious solutions, respectively, were coated onto glass which was coatedpreviously with the oxide (in conventional manner). The tin oxidecoating is of a thickness corresponding to a resistivity ofapproximately 100 ohms per square. After drying, a commerciallyavailable black lacquer is sprayed over the exposed surface of theliquid crystal-containing polymer matrix, and dried. The black lacqueris Spray On No. 6223008," which contains carbon black in an insulatingbinder matrix. Silver conductive paint is then applied to form anelectrode-on the black paint, and wires are attached to the silverelectrode and the tin oxide coating and connected to an alternatingcurrent source of electric potential (although either alternatingcurrent or direct current can be utilized). The resulting basicconfiguration is essentially the same as those shown in FIGS. 3 and 7.

Upon application of the alternating current potential, the reflectancefrom the area over the silver electrode when viewed with incident whitelight, shifts from green (first chromatic state) to blue (secondchromatic state). After the electric field is removed, the reflectancedoes not return to the original green color, but instead assumes a greyappearance (third chromatic state), which is in very good chromatic andconfigurational contrast to the green background areas which are notsubjected to the field.

On the reapplication of the electric field, that area of theencapsulated cholesteric liquid crystalline member through which thefield passes instantaneously turns to the blue color (second chromaticstate). Repeated, extensive cycling of the current on and off clearlydemonstrates and the cholesteric liquid crystal member possesses theability to be cycled for extended periods without breakdown or loss ofclearly discernible color contrast between the first, second and thirdchromatic states. 1

The pertinent compositional makeup of the liquid crystal materials andmatrix polymers used are tabulated below.

Gelatin Gelatin AE-4")."

The Elvanol polymers are polyvinyl alcohols marketed by E. l. du Pom deNemours 84 Company. Inc., Wilmington, Del. The differing numbersfollowing the designation Elvanol indicate specific products havingvarying viscosities. Elvanol 7124 is characterized by the fact that (a)a 4 percent. by weight, aqueous solution has a viscosity of 23 to 28centipoises at 25 centigrade, and (b) the material is 97.7 to 98.8percent hydrolyzed, i.e., that percentage of acetate or other chemicalgroups originally present in molecules of the material have beenconverted to hydroxyl groups. "Elvanol 5105" has a viscosity at 25"centigrade (4 weight percent aqueoussolution) to 4 to 6 centipoises andis 88 to 89 percent hydrolyzed; and a four weight percent aqueoussolution of Elvanol 7005" has a viscosity at 25 centigrade T4 to 6centipoises and is 99 to 100 per cent hydrolyzed.

"Gelatin Ali-4" is an acid extracted pigskin gelatin having a bloomstrength of about 28510 about 305 grams and an isoelectric point ofpl-l8 to 9.

With further samples on an. 55355555551; in:

dicated herein, the information present in the display device (viz, thecolored area(s) on a different colored background produced by theelectric potential) can be erased by application of heat to attain theisotropic melting point of the liquid crystal mixture in question, thusgenerating the entire film to its original green color first chromaticstate) when cooled again to room temperature. Another way ofregenerating the film is to regenerate it selectively by application ofthe heat or an electric current of sufficient intensity to raise thetemperature to the isotropic melting point of the liquid crystal mixturein selected areas only. In such a case, electrical current is passedthrough those resistive elements whose chromatic representation or imageis to be erased, causing the elements to be heated to the isotropictransition temperature. Hence, the erasure of the chromatic image can begeneral (to regenerate the entire film) or selective to a particulararea thereof. The electroconductive force or potential levels requiredto secure the second chromatic state and erasure of the third chromaticstate will depend mainly upon the thickness of the cholesteric liquidcrystalline member and the spacing of the conducting electrodes. Forexample, erasure can be achieved readily for l0 to 100 micron thickcholesteric liquid crystalline members by applying a potential of 100 to500 volts across the conductive elements to heat the elements to theisotropic melting point of a given liquid crystal mixture.

A variant of the article of Example 2 is prepared by applying the liquidcrystal droplet-polymer matrix emulsion coating on Mylar" film, paintingthe uncoated side of the Mylar" film black with Spray On No. 6223008"and pressing the liquid crystal droplet-polymer matrix side of the filmto the oxidecoated glass. The polyester ("Mylar") film serves as anadditional protective (barrier) film to protect the liquid crystaldroplets, viz, additional to the polymer matrix. Of course,otherequivalent protective polymeric materials can likewise be used. Theuse of such a protective film is preferable as it reduces the difficultysometimes encountered in painting the silver or other electroconductivematerial directly on the liquid crystal droplet-containing polymermatrix film. While the cause of this difficulty is not entirelyunderstood, it is believed due to some unconfined surface inclusions ofliquid crystal material in the matrix film which allow a solventcomponent(s) in the silver paint to dissolve in the unprotected liquidcrystals in the area(s) where such unconfined inclusions are present.

EXAMPLE 5 The procedure of Example 1 is repeated except using a Mylarprotective film and a mixture of cholesteric liquid crystallinematerials containing 73 weight percent cholesteryl nonanoate and 27weight percent cholesteryl chloride. Upon application of the electricfield a color change of from red (first chromatic state) to dull grey orblack (second chromatic state) was observed. It should be noted herethat the comparatively small amount of heat generated due to applicationof the electric field is insufficient to cause the liquid crystal tobecome liquid. Upon turning off the current, the color instantaneouslychanges from dull grey-black to a dull red (third chromatic state). Thisthird chromatic state is sufficiently sharp in contrast to that of thefirst chromatic state to enable clear distinction thereof to the nakedeye.

EXAMPLE 6 The procedure of Example l is repeated except using aprotective Mylar film and a cholesteric liquid crystalline mixturecontaining 79 weight percent of cholesteryl'nonanoate, 14 percent ofcholesteryl chloride and 7 weight percent of oleyl cholesterylcarbonate. The matrix film thickness is 80 microns. Upon application ofan electric potential of 100,000 volts per centimeter thickness of thecholesteric liquid crystalline member, the observed color of thecholesteric liquid crystalline mixture changes from green (firstchromatic state) to blue (second chromatic state). Uponremoval'of theelec- 7 tric field by shutting off the current, the third chromaticstate is instantaneously experienced, which is a grey-green color ofsufiiciently sharp contrast to that of the first chromatic state to bereadily observable to the naked eye.

EXAMPLE 7 Twenty-five copper plates 1 cm. X 2 cm. X 0.25 cm. are bondedto a plastic substrate in an evenly spaced 5 row-5 column matrix. Eachof the plates is soldered to a conductive lead wire extending throughthe substrate. The copper plates are sprayed with an insulating blacklacquer and a film of matrix confined-liquid crystal droplets preparednoted, with Example 6 is coated on the lacquer to a thickness of about100 microns.

The assembly is mounted in a vacuum chamber which is equipped with atransparent plastic port (window) such that the liquidcrystal-containing film is readily visible through the port. Theconductive lead wires are connected to vacuum tight electricalfeedthroughs in a plate at the opposite end of the vacuum chamber fromthe transparent port. A tungsten wire is mounted about two inches infront of the matrix (as noted e.g., in FIG. 4) and connected to a directcurrent power supply.

The chamber is pumped down to lXl-6 Torr vacuum and a current of about3.5 amps are passed through the tungsten wire causing it to glow red.When selected plates in the assembly are charged to a positive potentialof 700l500 volts, the electrons emitting from the hot wire are attractedto the surface of the liquid crystal-containing polymer matrix filmadjacent to the charged plates, and the electric field establishedbetween the surface electrons and the plate causes the liquid crystalsto change shade of color from green to dark grey-green. When the fieldis removed by removing the potential from the plate, the chromatic imagepersists but in a readily discernible different shade, viz, lightergrey-green.

EXAMPLE 8 A liquid crystal display utilizing a conventional cathode raytube (C.R.T.) output is prepared in the following manner. The targetface of the tube is coated on the interior surface with a transparentelectrode. A polymer matrix-bound film of field responsive cholestericliquid crystal droplets (as in Example 6) is coated in contact with thetransparent electrode as shown in FIG. followed by application of aprotective Mylar film. A black insulating lacquer film is sprayed on theMylar film. As mentioned previously, this black film is used to absorblight transmitted through the liquid crystal film in order to enhancethe contrast of color or shade of color scattered from the liquidcrystals.

lnasmuch as the liquid crystal is not in contact with another reflectivesurface on its interior surface when used in a C.R.T.), this blackinsulator film is probably optional with this device.

After coating of the black film, the tube is pumped down to suitablevacuum and can be operated as a conventional video tube. The transparentelectrode on the face plate is held as a positive potential and theelectron beam is caused to trace the desired pattern on the liquidcrystal-containing film.

The local fields set up between the electrons trapped at the interiorsurface of the liquid crystal (or black insulator) and the positivelycharged transparent electrode cause the liquid crystals to change colorin those areas and form a visible pattern which may be observed throughthe face plate and the transparent electrode. The pattern is optionallycomparatively permanent, viz, subject to erasure, and one sweep of theelectron beam will suffice to establish the image. This image can beerased generally or selectively (in certain areas thereof) by heatingthe liquid crystal to its isotropic transition temperature. The colorshade changes are the same as noted above in Example 7.

Since the mechanism requires only that the electrons be deposited on theliquid crystal surface, the electron beam can be of much lower energythan normally required for stimulation of a phosphor (most often usedfor C.lifliiniaghgi 'very weak color contrasts with conventionalphosphors at the same conditions.

EXAMPLE 9 This device is similar in many respects to that describedunder Example 8 except that the liquid crystal containing, polymermatrix bound film is applied to the exterior of the C.R.T.

The face plate of the C.R.T. is prepared with a matrix of closely spacedconductive wires imbedded in it with one end of the wires exposed to theinterior of the tube and the other end flush to the exterior surface ofthe faceplate, as shown in FIG. 6. The exterior surface is painted witha black insulating film if desired, and then a film of cholestericliquid crystal (as in Example 6) is coated on the black insulatorfollowed by optional application of a protective Mylar" film.

A transparent plate with a transparent electrode coated on its surfaceis attached to the tube with the conducting surface in contact witheither the protective Mylar" film (if used) or the liquid crystal film.

The transparent electrode is charged positively and the C.R.T. isoperated in a conventional manner such that an electron beam strikes thewire ends extending through the faceplate in the pattern desired. Theelectrons are conducted through the individual wires of the faceplate tothe surface of the cholesteric liquid crystal containing film whichexhibits a color change in the areas between the wires which have beencharged by the electron beam and the positively charged transparentelectrode in the same manner as noted above in Example 7.

While the above Examples illustrate the invention in great detail, itshould be understood that the present invention in its broadest aspectsis not necessarily limited to the specific materials, conditions, andstructural embodiments set forth therein.

What I claim is: 7 v p 1. An article of manufacture comprising a pair ofspaced electrodes and located there between a cholesteric liquidcrystalline member chromatically responsive to the electric fieldimposed due to said electrodes and comprised of a plurality ofindividual minute, naked droplets of cholesteric liquid crystal materialconfined in a substantially continuous polymeric matrix.

2. An article as in claim 1 wherein said electric field ranges fromabout 10,000 to about 1,000,000 volts per centimeter of thickness ofsaid cholesteric liquid crystalline member.

3. An article as in claim 1 wherein one of said electrodes issubstantially transparent.

4. An article as in claim 3 wherein includes an opaque contrastingbackground located behind said cholesteric liquid crystalline member.

5. An article as in claim 4 which includes a substantially transparentprotective covering for said substantially transparent electrode.

6. An article as in claim 4 which includes a protective polymer filmlocated intermediate said opaque contrasting background and saidcholesteric liquid crystalline member.

7. An article as in claim 6 wherein said droplets are uniformlydistributed within said polymeric matrix.

8. An article as in claim 6 wherein said droplets have average diametersranging from about i to about 30 microns.

9. An article as in claim 6 wherein said cholesteric liquid crystallinemember contains from about 30 to about weight percent cholesteric liquidcrystal material, based on the total weight of said matrix and liquidcrystal material.

10. An article as in claim 6 wherein the average thickness of saidliquid crystalline member ranges from about 0.001 to about 0.05centimeters.

11. A display device for chromatically representing a configurationestablished by an electric field comprising a first electrode and asecond electrode spaced therefrom, said first electrode being closer toa viewing agency than said second electrode, and a cholesteric liquidcrystalline member located between said electrodes and chromaticallyresponsive to said electric field said member comprised of a'profusionof individual, minute, naked droplets of cholesteric liquid crystalmaterial confined in a substantially continuous, solid polymeric matrix.V v 7 12. A display device as in claim 11 wherein said firstelectrodeissubstantially transparent.

13. A display device as in claim li wherein" said substantiallytransparent first electrode has a substantially transparent protectivecovering. V

14. A display device as in claim 11 which includes an opaque contrastingbackground located between said cholesteric liquid crystalline memberand said second electrode.

I ingbackground said cholesteric liquid crystalline member. g

16. A display device having polychromatic capability for chromaticallyrepresenting an optionally comparatively permanent yet thermallyerasable configuration established by an electric field in optionalconjunction with an independently operable yet thermally erasabletransient, thermally operable, separate display means, said devicecomprising a transparent support; support; a transparentelectroconductive coating on said support; conductive electrodes incontact with said coating and operatively connected by leads to anelectric field source; an insulator film having a cholesteric liquidcrystal member in intimate proximity to said film and said coating,

.said cholesteric liquid crystal member comprised of a profusion ofindividual naked droplets of cholesteric liquid crystal material,chromatically responsive to an electric field, confined in asubstantially continuous solid polymeric matrix; and at least oneelectrically conductive resistive element in thermally responsiveassociation with said cholesteric liquid crystal member, each saidresistive element having a separate pair of conductive leads connectedto a current source operable independently from said electric fieldsource and wherein said cholesteric liquid crystal member ischromatically responsive to both an electric field and thermally energyapplied thereto.

17. A display device as in claim 16 wherein said insulator film isopaque.

1. An article of manufacture comprising a pair of spaced electrodes andlocated there between a cholesteric liquid crystalline memberchromatically responsive to the electric field imposed due to saidelectrodes and comprised of a plurality of individual minute, nakeddroplets of cholesteric liquid crystal material confined in asubstantially continuous polymeric matrix.
 2. An article as in claim 1wherein said electric field ranges from about 10,000 to about 1,000,000volts per centimeter of thickness of said cholesteric liquid crystallinemember.
 3. An article as in claim 1 wherein one of said electrodes issubstantially transparent.
 4. An article as in claim 3 wherein includesan opaque contrasting background located behind said cholesteric liquidcrystalline member.
 5. An article as in claim 4 which includes asubstantially transparent protective covering for said substantiallytransparent electrode.
 6. An article as in claim 4 which includes aprotective polymer film located intermediate said opaque contrastingbackground and said cholesteric liquid crystalline member.
 7. An articleas in claim 6 wherein said droplets are uniformly distributed withinsaid polymeric matrix.
 8. An article as in claim 6 wherein said dropletshave average diameters ranging from about 1 to about 30 microns.
 9. Anarticle as in claim 6 wherein said cholesteric liquid crystalline membercontains from about 30 to about 95 weight percent cholesteric liquidcrystal material, based on the total weight of said matrix and liquidcrystal material.
 10. An article as in claim 6 wherein the averagethickness of said liquid crystalline member ranges from about 0.001 toabout 0.05 centimeters.
 11. A display device for chromaticallyrepresenting a configuration established by an electric field comprisinga first electrode and a second electrode spaced therefrom, said firstelectrode being closer to a viewing agency than said second electrode,and a cholesteric liquid crystalline member located between saidelectrodes and chromatically responsive to said electric field saidmember comprised of a profusion of individual, minute, naked droplets ofcholesteric liquid crystal material confined in a substantiallycontinuous, solid polymeric matrix.
 12. A display device as in claim 11wherein said first electrode is substantially transparent.
 13. A displaydevice as in claim 12 wherein said substantially transparent firstelectrode has a substantially transparent protective covering.
 14. Adisplay device as in claim 11 which includes an opaque contrastingbackground located between said cholesteric liquid crystalline memberand said second electrode.
 15. A display device as in claim 14 whichincludes a protective polymer layer located intermediate said opaquecontrasting background said cholesteric liquid crystalline member.
 16. Adisplay device having polychromatic capability for chromaticallyrepresenting an optionally comparatively permanent yet thermallyerasable configuration established by an electric field in optionalconjunction with an independently operable yet thermally erasabletransient, thermally operable, separate display means, said devicecomprising a transparent support; support; a transparentelectroconductive coating on said support; conductive electrodes incontact with said coating and operatively connected by leads to anelectric field source; an insulator film having a cholesteric liquidcrystal member in intimate proximity to said film and said coating, saidcholesteric liquid crystal member comprised of a profusion of individualnaked droplets of cholesteric liquid crystal material, chromaticallyresponsive to an electric field, confined in a substantially continuoussolid polymeric matrix; and at least one electrically conductiveresistive element in thermally responsive association with saidcholesteric liquid crystal member, each said resistive element having aseparate pair of conductive leads connected to a current source operableindependently from said electric field source and wherein saidcholesteric liquid crystal member is chromatically responsive to both anelectric field and thermally energy applied thereto.
 17. A displaydevice as in claim 16 wherein said insulator film is opaque.